It is well known that individual fuel cells, when a fuel cell stack is under a load, that do not receive an adequate, uniform flow of hydrogen will undergo local reverse currents which causes corrosion of the cathode catalyst layer. The corrosion degrades the power output performance of the fuel cell stack.
To assure adequate fuel, and improve the humidity thereof, fuel recycle gas is transferred from the fuel flow field exits to the fuel flow field inlets. This causes build-up of inert (non-fuel) gases in the flow, such as nitrogen passing from air in the cathode, through the porous membrane, to the anode.
Purging of some amount of the fuel flow, to ambient or a burner, is used to reduce the inerts in the recycle gas.